Skin is composed of three superposed layers that are, from surface to body depth, epidermis, dermis and hypodermis.
Epidermis can be divided, according to morphological and histological criteria, into four layers, from the deepest to the outermost: the basal lamina and the spinosal layer (who form the deep epidermis), and the granular layer (superficial epidermis) and the corneal layer (or stratum corneum). Epidermis is a keratinized stratified pavimentous epithelium mostly composed of Merkel and Langerhans cells. Epidermis is in contact with external environment. One of its roles is to protect the organism from dehydration and chemical, mechanical or infectious exterior aggressions.
Dermis is an irrigated connective tissue mostly composed of fibroblasts and of an extracellular matrix made of muccopolysaccharides and of macromolecules such as collagen, elastin and fibronectin fibers. It assumes a nourishing and support function with regards to epidermis.
Skin is known to have tendency to drying due to environmental, psychological and hormonal factors. Now, it is important that skin be well moisturized and does not suffer a water loss that would lead to skin wilting and drying. Cutaneous dehydration shows in tightening, loss of flexibility and elasticity. Skin becomes rough, even scaly. Treating cutaneous dryness is an essential challenging: enabling the corneal layer to keep its suppleness and its barrier function is also a more global way to protect the underlying dermis and to prevent skin ageing.
Different moisturizing products currently exist on the cosmetic market. For example, occlusive substances can be used that delay water evaporation, humectants can be used that capture atmospherical water, or gelified polymers can be used. Cosmetics market is still demanding new alternatives solutions for keeping a supple, flexible and soft skin irrespective of age.
Among the hydration actives often used, betaine (trimethylglycine) is found. In this regard Japanese patent application JP 09095411 discloses compositions for skin care that comprise a betaine and erythritol combination. However, the inventors have discovered surprisingly that a combination of homarine/erythritol has unexpected synergistic osmoprotector effects by comparison to a combination of betaine/erythritol.
Homarine is a cyclic zwitterion. It is also an osmolyte meaning that it is significantly mobilized by the cell to maintain or adjust the osmotic pressure and the volume of the cell. These osmolytes found in their natural state in various living organisms (algae, plants, bacteria . . . ) are synthesized when the organism is subjected to different stress; they are cellular homeostasy regulators.
Erythritol is a water-soluble polyvalent alcohol having several hydroxyl functions. That sugar is present in eukaryotes: in many yeast species, in Aspergillus, Platymonas . . . 
To the knowledge of the inventors, no prior art document discloses the synergy of osmoprotective and/or hydration activity of the homarine/erythritol combination.
Thus, the main object of the present invention consists of a cosmetic or dermopharmaceutic composition for topical use comprising in a physiologically acceptable medium as active ingredients (a) at least homarine, one of its salts and/or one of its analogs of C2-C6 N-alkyl type, preferably selected from derivatives of N-ethyl, N-propyl and N-butyl type, and (b) at least erythritol.
One of the advantages of the present invention is that it helps regulate ion efflux in skin cells, provides protection for these cells towards osmotic shocks or environmental stress, and increases the cutaneous water holding capacity.
The invention is also directed to a cosmetic for improving the skin and scalp general state, and more particularly for preventing or treating cutaneous dehydration, for improving cutaneous hydration, reinforcing the cutaneous barrier function, comprising the topical application on skin and/or on scalp of a healthy and effective amount of a composition comprising in a physiologically acceptable medium a combination of homarine and of erythritol.
According to the invention, “physiologically acceptable medium” means, without limitation, an aqueous or hydroalcoholic solution, a water-in-oil emulsion, an oil-in-water emulsion, a microemulsion, an aqueous gel, an anhydrous gel, a serum or a vesicle dispersion. “Physiologically acceptable” means that the described compositions or compounds are suitable for use in contact with mammalian mucosals, nails, scalp, hair, hairs and skin, and more particularly human, without undue toxicity, incompatibility, instability, allergic response, and the like.
In the context of the present invention, homarine and erythritol can be obtained from any supply source, in particular by hemi-chemical synthese way, chemical synthese way, enzymatic way, by any other mean usable for obtaining them in the ended product at reasonable costs for an industrial application.
The homarine amount that can be used in the context of the invention may vary to a large extend and may be preferably from 0.00001% to 50%, preferably from 0.0001% to 30%, more preferably from 0.001% to 10% by weight with respect to the total composition weight.
The erythritol amount that can be used in the context of the invention may vary to a large extend and may be preferably from 0.00001% to 80%, preferably from 0.001% to 50%, more preferably from 0.01% to 30% by weight with respect to the total composition weight.
According to the invention, the ponderal ratio homarine/erythritol may preferably be from 1:1000 to 10:1, preferably from 1:1000 to 1:1, and more preferably from 1:100 to 1:10.
All percentages and ratios used here are by weight of the total composition and all measures are made at 25° C. unless it is otherwise specified.
It is possible to integrate in the composition of the invention products already known as having an activity helping, improving or restoring cutaneous hydration. Thus, according to a particular embodiment, the composition of the present invention may further comprise at least one additional active ingredient selected from the group consisting of moisturizing agents, humectant agents, occlusive agents, desquaming agents, agents acting on the cutaneous barrier function, UV filters, agents regulating cellular homeostasy, film formers, agents regulating aquaporin expression, anti-aging agents, anti-wrinkle agents, anti-oxidizing agents, anti-inflamatory agents, depigmenting or propigmenting agents, self-tanning agents, anti-glycation agents, NO-synthase inhibitors, agents stimulating dermal or epidermal macromolecule synthesis and/or preventing their degradation, agents stimulating fibroblast and/or keratinocytes proliferation or stimulating keratinocytes differenciation, anti-pollution and/or anti-radicals agents, agents acting on microcirculation, anti-vergeture agents, agents acting on energetical metabolism of cells, anti-acne agents, agents promoting lymphatic drainage, anti-hairs regrowth agents and mixture thereof.
Non limiting examples of these agents are: betaine, glycerol, Actimoist Bio 2™ (Active Organics), AquaCacteen™ (Mibelle AG Cosmetics), Aquaphyline™ (Silab), AquaregulK™ (Solabia), Carciline™ (Greentech), Codiavelane™ (Biotech Marine), Dermaflux™ (Arch Chemicals Inc.), Hydra'Flow™ (Sochibo), Hydromoist L™ (Symrise), RenovHyal™ (Soliance), Seamoss™ (Biotech Marine), Essenskin™ (Sederma) and Moist 24™ (Sederma).